1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor and an electrophotographic imaging apparatus using the photoreceptor. More particularly, the invention relates to an electrophotographic photoreceptor which includes naphthalenetetracarboxylic acid diimide derivatives as an electron transporting material in a charge generating layer to enhance electrostatic properties such as photosensitivity and exposure potential, and an electrophotographic imaging apparatus employing the same.
2. Description of the Related Art
In electrophotography, for example, laser printers and copy machines, an electrophotographic photoreceptor includes a photosensitive layer formed on an electrically conductive substrate, and can be in the form of a plate, a disk, a sheet, a belt, or a drum, etc. In an electrophotographic photoreceptor, a surface of the photosensitive layer is first electrostatically charged uniformly, and then the charged surface is exposed to a pattern of light, thus forming an image. The light exposure selectively dissipates the charge in the exposed regions where the light strikes the surface, thereby forming a pattern of charged and uncharged regions, which is referred to as a latent image. Then, a wet or dry toner is applied in the vicinity of the latent image, and toner droplets or particles deposit in either the charged or uncharged regions to form a toner image on the surface of the photosensitive layer. The resulting toner image can be transferred and fixed to a suitable ultimate or intermediate receiving surface, such as paper, or the photosensitive layer can function as the ultimate receptor for receiving the image.
Electrophotographic photoreceptors are generally categorized into two types. The first has a two-layered type that includes a charge generating layer having a binder resin and a charge generating material (CGM), and a charge transporting layer having a binder resin and a charge transporting material (mainly, a hole transporting material (HTM)). In general, the laminated type electrophotographic photoreceptor is used in the fabrication of a negative (−) type electrophotographic photoreceptor. The other type is a single layered type in which a binder resin, a CGM, an HTM, and an electron transporting material (ETM) are contained in a single layer. In general, the single layered type photoreceptor is used in the fabrication of a positive (+) type electrophotographic photoreceptor.
The charge generating material generates charge carriers, that is holes and/or electrons upon light exposure. The charge transporting material contains at least one of the charge carriers and transports them through a charge transporting layer in order to easily discharge the surface charge of a photoreceptor.
For the charge generating layer in the two-layered type electrophotographic photoreceptor, the amount of the charge generating material is generally abundant to form an electrophotographic photoreceptor having high photosensitivity. However, when the amount of the charge generating material is too high, the stability of the coating slurry for forming the charge generating layer deteriorates so that the coating quality for the charge generating layer may be degraded, and the adhesion between the charge generating layer and an electrically conductive substrate, and the adhesion between the charge generating layer and the charge transporting layer may be degraded. On the contrary, when the amount of the charge generating material is too small, the stability of the coating slurry for forming the charge generating layer, the coating quality for the charge generating layer, the adhesion between the charge generating layer and an electrically conductive substrate, and the adhesion between the charge generating layer and the charge transporting layer are improved, but electrostatic properties of the electrophotographic photoreceptor are drastically deteriorated, for example, the degradation of the photosensitivity of the electrophotographic photoreceptor and the increase of exposure potential. In addition, regardless of the amount of the charge generating material in the charge generating layer, electrons are not smoothly transported through the charge generating layer so that the electrostatic properties of the electrophotographic photoreceptor are liable not to be fully exhibited, for example, low photosensitivity and high exposure potential of the electrophotographic photoreceptor. In particular, the degradation of the electrostatic properties due to the difficulty of the electron transportation in the charge generating layer is more serious when the thickness of the charge generating layer is increased in order to obtain high photosensitivity because charges are mainly generated at the upper portion of the charge generating layer.
To solve these problems, electrophotographic photoreceptors are disclosed in U.S. Pat. Nos. 5,547,790, 5,571,648, and 5,677,094.
U.S. Pat. No. 5,547,790 discloses an electrophotographic photoconductor comprising an electroconductive support and a photoconductive layer formed thereon. The photoconductive layer includes at least a charge generation layer comprising a charge generating material selected from the group consisting of azo pigments, perinone pigments and squaraines. The photoconductive layer also includes a polymeric charge transporting material, and a charge transport layer comprising a polymeric charge transporting material. The polymeric charge transporting material in said charge generation layer is selected from the group consisting of polysilylene, a polymer having a hydrazone structure on the main chain and/or side chain thereof, and a polymer having a tertiary amine structure on the main chain and/or side chain thereof. The polymeric charge transporting material in said charge transport layer is selected from the group consisting of polysilylene, a polymer having a hydrazone structure on the main chain and/or side chain thereof, and a polymer having a tertiary amine structure on the main chain and/or side chain thereof.
U.S. Pat. No. 5,571,648 discloses an electrophotographic imaging member comprising a support substrate having a two electrically conductive ground plane layers comprising a layer of zirconium over a layer of titanium, a hole blocking layer, an adhesive layer comprising a copolyester film forming resin, and an intermediate layer in contact with said adhesive layer. The intermediate layer is a film forming carbazole polymer. A charge generation layer is also provided comprising perylene or a phthalocyanine particles dispersed in a film forming polymer binder blend of polycarbonate and carbazole polymer. A hole transport layer is provided that is substantially non-absorbing in the spectral region at which the charge generation layer generates and injects photogenerated holes but being capable of supporting the injection of photogenerated holes from the charge generation layer and transporting said holes through the charge transport layer.
U.S. Pat. No. 5,677,094 discloses an electrophotographic photoconductor comprising an electroconductive support and a photoconductive layer formed on the electroconductive support and including a charge generation layer and a charge transport layer. The charge generation layer is a first polymeric charge transporting material having an ionization potential of 6.0 eV or less. The charge transport layer is a charge transporting small molecule and a binder.
In the electrophotographic photoreceptors disclosed in the above-described US Patents, the hole transporting material is further included in the charge generating layer in addition to the charge generating material to improve the electrostatic properties thereof. However, the electrostatic properties of the electrophotographic photoreceptor should be further improved.